In transparent (or partially transparent) optical communication networks, a link between two nodes is most often composed of several segments. A segment is a length composed off a single type of optical fibre. Due to history of network deployment, segments composing a link are not necessarily of the same type. Said types of optical fibre may be, among others, G.652 or G.655 compliant types, such as e.g. Single Mode Fibre, SMF, type or Large Effective Area Fibre, LEAF, type.
For a given minimum quality of transmission, QoT, to know if a transmission can be guaranteed, two methods are actually known and used.
A first method, known as “QoT estimator”, is an analytic method. It typically needs all physical characteristics of all optical fibres along a link. Said first method enables a fine knowledge of the QoT, whatever fibre types being used for transmission. Such a method may e.g. use weighted non linear phase, when different types of fibre are used. The major drawback of this first method is the important amount of information typically necessary to compute and that has to be spread out across the control plane of the network.
A second method, known as “max reach”, considers, for a given QoT, a maximum length of optical fibre that can be travelled by a signal. Said second method typically requires only knowing a maximum distance a signal can travel through a link before being too distorted and showing an error level too high to comply with said QoT. This rougher second method is typically easier to compute. However, as actually applied, it appears somewhat simplistic in that it is based on the hypothesis that the types of fibre encountered through a link are homogenous. Only one type of fibre is typically considered. To be sure to guarantee said QoT, the single maximum length of optical fibre is determined by considering the most degrading type of optical fibre, even if a link is mainly composed of lesser degrading type of optical fibre. Such a method, for link comprising heterogeneous types of optical fibre typically leads to an undesired result.
If e.g. said method is used to place a regenerator just before said maximum distance is reached through said link, it typically leads to placing more regenerators than required.